1. Field of the Invention
The present invention relates to a system for operating a cylinder valve of an internal combustion engine, and more particularly to a variable valve timing and lift system which can change both valve timing and valve lift.
2. Description of the Prior Art
JP-A 55-137305 discloses a variable valve timing and lift system. It includes a camshaft, a control rod with axially spaced eccentric cams, and a pivot structure. The pivot structure supports valve operating (VO) cams for pivotal motion above valve lifters of cylinder valves. Springs are mounted to the VO cams, respectively. Each of the springs biases one of the corresponding rocker cams toward its rest position where the associated cylinder valve closes. Rocker arms operate the VO cams, respectively. The eccentric cams, which are in rotary unison with the control rod, bear the rocker arms, respectively. An axis of each of the eccentric cams serves as the center of drive of the corresponding one of the rocker arms. Cams on the camshaft operate the rocker arms, respectively. An electronic control module (ECM) is provided. Sensors on the engine send information on engine speed, engine load, vehicle speed, and coolant temperature to the ECM. At a predetermined switchover point, the ECM sends a signal to an actuator for the control rod. As the actuator turns the control rod, the eccentricity of each of the eccentric cams with respect to an axis of the control shaft changes. This alters the position of pivot center of the rocker arms relative to the position of pivot center of the VO cams. This causes variation in valve timing and lift of each of the cylinder valves.
According to this known system, the camshaft is not mounted above the cylinder valves. This arrangement has a potential problem in that considerable modification of the conventional overhead camshaft engine is required to install the camshaft. Besides, the pivot structure and camshaft require a considerable space to install.